The use of horizontal chemical vapor deposition (CVD) epitaxial reactors to deposit materials on semiconductor wafers is well known. One such horizontal reactor is comprised of a quartz tube in which a planar graphite susceptor, having a plurality of wafers thereon, is positioned. Banks of infrared (IR) lamps or radio frequency (RF) coils, mounted outside the tube are activated to heat wafers as well as the susceptor which, in turn, also heats the wafers. A flow of silicon-bearing gaseous compounds in a hydrogen ambient are then directed longitudinally into the tube. When the wafers reach a certain temperature, the silicon compounds react on. The foregoing problem has been solved by the apparatus of the present invention. The apparatus comprises a chemical vapor deposition reactor having an elongated member positioned therein and adapted to receive a semiconductor wafer. Separate means are provided to heat the wafer and to direct a reactant-containing gas to deposit reactants on the surface of the heated wafer. Also, means are provided for directing a reactant-free gas between reactant-containing gas and the inner surface of the hollow member to substantially eliminate the deposition of reactants thereon.
If RF coils are used, the silicon material will also deposit on the inside surface of the tube wall, however, the aforementioned positive feedback situation will not occur as the RF does not couple significantly to the silicon. However, such deposition does increase the frequency of cleaning required to provide an effective CVD process.
One technique used in an attempt to solve this problem is to direct streams of cool air at the outside surface of the tube to stop the silicon deposition on the inside surface of the tube wall. Although such a technique does tend to decrease the undesired deposition, unfortunately, some deposition still occurs with the attendant problems.
Accordingly, there is a need for a technique for substantially eliminating the deposition of silicon on the inside surface of a horizontal chemical vapor deposition reactor during the operation thereof.